The present invention relates to an omnidirectional camera which takes images of an omnidirectional landscape by a plurality of cameras and which measures a position where images are taken.
In recent years, with spread of a navigation system, not only a positional information as an information of an electronic map but also an image information of a target, a building, a construction, and a landscape around a road or the like are required. Therefore, a measurement for acquiring a positional data as a map information is carried out by using a GPS (Global Positioning System) and, at the same time, an image data is acquired by using an omnidirectional camera.
In recent years, there has been developed a data collection system in which a GPS is mounted in a movable vehicle such as a vehicle, a camera or a laser surveying device (a laser scanner) is mounted, a three-dimensional data of a construction or a building in urban space is collected and images are also collected, and this data collection system is made good use of the preparation of a map data to be used for car navigation and other purposes.
However, in a case of a conventional system, a GPS antenna and a camera are independently provided, there is a problem corresponding to an arrangement of the GPS antenna.
For example, in a case where the GPS antenna is provided near and above the camera, this arrangement is ideal for receiving a GPS signal, but the GPS antenna itself is reflected in the camera which takes images in a zenith direction, which obstructs a photographing of a landscape behind the GPS antenna.
In the case described above, since the GPS antenna is positioned near the camera and a relative positional displacement hardly occurs, a relative positional relationship can be calculated based on an initial design value, but the positional relationship between both the GPS antenna and the camera is apt to vary due to an error caused at a time of an installation.
In a case where the GPS antenna is provided above the camera via a pole at a position apart from the camera, there is no problem in receiving the GPS signal, but the GPS antenna and the pole supporting the GPS antenna are reflected in the camera, which obstructs a viewing field.
Also, in a case where the GPS antenna is provided below the camera at a position apart from the camera, since the GPS antenna is positioned below the system, components and devices, e.g. a camera and others may be an obstacle at a time of receiving a GPS signal.
Further, in the case described above, the GPS antenna is separated from the camera, and the GPS antenna and the camera are individually installed at the time of the installation. Therefore, a displacement occurs due to an installation error every time. Accordingly, a distance between the GPS antenna and the camera is measured every time the installation is carried out, and then a relative positional relationship is calculated based on a position of the GPS antenna on a photographed image. Therefore, a positional relationship between the GPS antenna and the camera is apt to vary due to a measurement error of a distance between the GPS antenna and the camera or a measurement error of the GPS antenna position on an image and so on.
Further, in a position measurement by using the GPS, in a case where the receiving of the GPS signal is interrupted because of a state of being in a shade of a building or a mountain or the like, a self-position cannot be determined. Therefore, an inertial measurement unit (IMU) is mounted, and the position measurement using the IMU is carried out while the position measurement cannot be carried out by using the GPS. In this case, the IMU is installed at a position apart from the camera. For example, the IMU is installed at a position that is several tens of centimeters apart from the camera.
Also, in a case where the omnidirectional camera is mounted on a ceiling portion of a vehicle and a map data is acquired, when the vehicle with the camera decelerates, the vehicle tilts forward at a pitch angle corresponding to an acceleration around pitch center as a center and when the vehicle turns, e.g. in a counterclockwise direction, the vehicle tilts toward a right side at a roll angle corresponding to the acceleration around roll center as a center. Therefore, in a case where the pitch center or the roll center is provided in a lower portion of the vehicle and the camera and the IMU are disposed at positions apart from each other, when the vehicle accelerates/decelerates or turns, the IMU receives an acceleration different from an acceleration of the camera, and there is a problem that an accurate position of the camera cannot be determined.
It is noted that JP-A-2010-38822 discloses an omnidirectional camera with a GPS and a spatial data collection device that prevent deviation of a reference position of a GPS antenna and a reference position of an image and enable acquisition of images in all directions except an upper direction even when the reference position of the GPS antenna is adjusted to coincide with the image reference position of the camera and a direction of a vehicle changes or the vehicle is inclined.